The present invention relates to a reference system for measuring the vertical and horizontal position of the rails of a railroad track, and more particularly to a transducer for use in such a system.
Chord reference systems are well known in the railroad industry. These reference systems are carried by a track maintenance vehicle to measure the vertical and horizontal disposition of the rails of a railroad track. For example, one such system includes a pair of horizontal height-measuring reference chords extending over each rail and a third horizontal lateral-measuring reference chord extending down the center of the vehicle. A carriage rides along the rails and carries a plurality of transducers-one or more for each chord. Each transducer includes an arm that rides on one of the reference chords to sense relative movement between the chord and the carriage.
As the maintenance vehicle moves along the track, the transducers measure the displacement of the reference chords with respect to the carriage riding on the track. The height-measuring transducers generate a signal indicative of the vertical undulations in the rail. The lateral-measuring transducers generate a signal indicative of the horizontal or lateral displacement of the rail. The transducer signals can be processed according to a variety of well known algorithms to acquire important information about the position and alignment of the rails and even to reconstruct a mathematical model (called a profile) of the track.
Typically the arm of each transducer is counterbalanced to offset its weight upon the-chord so that the chord can remain undeflected. This is particularly true for the height-measuring transducers. The need to counterbalance is commonly accepted wisdom in an attempt to acquire as accurate data as possible. However, counterbalancing has its drawbacks. First, counterbalancing structures are relatively delicate and not particularly well-suited to the rigors of railroad track maintenance. Second, a loss of tension or a break in the chord will not be readily detectable by the transducer because the arm will simply remain in place. Third, there is typically enough friction and inertia between the transducer arm and the transducer housing so that movement of the housing (e.g. in response to the rise and fall of the rails) imparts some movement to the arm, thereby introducing some inaccuracy in the measurements.